1. Field of the Invention
This invention relates to a longitudinally extending constant speed decline belt conveyor which includes a retarding apparatus to prevent loads traversing the same from travelling over the conveyor belt too rapidly. More particularly, the invention relates to a braking system in which an endless traction belt is utilized to apply a braking force to the bottom surface of the load. The invention addresses the unique problem of belt conveyors which operate in a decline mode. In other words, the conveyor is one where the loading end of the conveyor is higher than the discharge end.
2. Description of the Prior Art
Prior art devices are of two types, powered belt conveyors and non-powered roller conveyors. As shown in FIG. 1, belt conveyors utilize a motor and gear train which act as braking devices to prevent the objects that are being conveyed downhill from increasing in speed and running away. The head pulley, which is located at the top of the conveyor, is connected to the motor by chains or belts and the motor provides retarding torque to assure that the conveyed materials move down hill at a consistent speed. Such arrangements are expensive, require external power, and their mounting requires additional space. Moreover, the complex set of parts to accomplish this requires frequent maintenance and repair.
In general, the non-powered, gravity fed roller conveyors utilize a special speed control roller inserted among the plurality of rollers on the conveyor. These speed control rollers produce a braking force and control the maximum rate of advance of the load being conveyed down the gravity roller conveyor. These speed control or retarding rollers often were liquid filled as shown in U.S. Pat. No. 2,618,370 to Orwin, U.S. Pat. No. 3,511,350 to Stein, U.S. Pat. No. 2,607,459 to Ludwig et al, and U.S. Pat. No. 3,399,752 to Orwin. Non-liquid filled braking devices such as that shown in U.S. Pat. No. 3,655,021 to Froio have also been utilized.
One of the difficulties encountered in utilizing any of these prior art braking devices is that a braking action is developed only when the bottom surface of a load engages the braking roller. When such a load bottom surface moves across a braking roller, a braking action is applied only for the time of engagement between the roller engagement support surface and the braking roller.
The net result of using such a system is that the speed of the load travelling over the gravity roller conveyor is not properly controlled after the load moves past the brake roller. This results in damage to the loads being transported or to the gravity roller conveyor itself. While it is possible to increase the number of braking rollers utilized in a given conveyor system, this solution has been found to be very costly and complex. An example of this is disclosed in Newman, U.S. Pat. No. 4,383,598, which involved many brake units. However, this patent requires mechanical or electronic sensors and electronic circuitry which activates pneumatic cylinders.